Various applications utilize MR heads to sense the presence of a magnetic field. For example, many current hard disc drive data storage systems use heads employing high sensitivity giant magnetoresistive (GMR) readers to read the data from the recording media. Future generation MR heads are expected to use current perpendicular-to-plane (CPP) type readers or sensors. Examples of this type of CPP reader include tunneling magnetoresistive (TMR) readers and CPP spin valve readers. In these future MR heads, as well as in current MR heads, in order to read the data, current is passed through the MR element of the reader. The power dissipated by the MR element generates heat. The heat raises the working temperature of the MR head. The increase in the temperature in the MR head adversely affects the lifetime of the MR head.
When an MR reader or sensor is exposed to an ESD, or even a voltage or a current input larger than that intended under normal operating conditions, referred to as EOS the MR reader may be damaged. As MR readers are made smaller and more sensitive, their susceptibility to ESD or EOS has increased and the voltage at which damage may occur has continued to fall. For example, the family of heads using MR readers in early development of this technology had a failure voltage of approximately 2 volts. That number has dropped to below 0.5 volt for TMR read heads, and can be excepted to continue to fall with technological advances. Therefore, methods to prevent ESD or EOS damage to MR readers or sensors during manufacturing processes is very important.
Numerous techniques for providing ESD or EOS protection have been utilized in the prior art. Some of these techniques utilize diodes or metal oxide semiconductor field effect transistors (MOSFETs) to shunt current away from the MR element of the reader. However, this approach has significant disadvantages. In diode or MOSFET approaches, the turn-on voltage is difficult to control, and may not be small enough to protect the MR element. Also, fabricating a diode or MOSFET with the MR reader significantly increases the number of process steps, since the diode or MOSFET does not have the same structure (number of layers, thickness of layers, materials, etc.) as the MR reader.
Another prior art approach to providing ESD or EOS protection is to fabricate a resistor in parallel with the MR reader. If the protective resistor has a resistance which is significantly smaller then the resistance of the MR reader, a large portion of the damaging current will be shunted across the protective resistor. However, this technique presents challenges and provides disadvantages as well. First, fabrication of a parallel resistor can, in many instances, add additional process steps to the steps required to fabricate the MR reader. Also, the addition of a parallel protective resistor can make it difficult to test the MR reader during the fabrication process. Further, a parallel resistor provides little information to aid in the fabrication process. For example, since a parallel resistor does not react in the same manner to external stimulus, such as the presence of a magnetic field, inclusion of such a resistor renders it more difficult to analyze the response of the MR reader to the stimulus during manufacturing.
Yet another prior art approach to providing ESD or EOS protection is to short out the MR sensor element of the reader. While shorting out the MR sensor element provides very good ESD or EOS protection, it also removes the possibility of testing the MR reader after the short is applied. Ideally, as the MR head goes through the wafer fabrication, slider fabrication, and related processes, it is beneficial to be able to test the MR head at various points.
A technique for providing ESD and EOS protection during MR head fabrication, which addresses one or more these problems or other problems not discussed, would be a significant improvement in the art.